An LACP (Link Aggregation Control Protocol, link aggregation control protocol) is a protocol for achieving dynamic link aggregation and disaggregation, and the aggregation is to improve transmission bandwidth and reliability of the system. Under the control of the LACP protocol, multiple links (member link) aggregate to a logic link with a higher bandwidth, the logic link is called an aggregation group and the link including the aggregation group is called an LACP link. The number of the member links aggregated in one aggregation group is usually determined according to the bandwidth requirement of the traffic.
Generally, the number of active interfaces at one end of the aggregation group member link is at least larger than or equal to a preset minimum active link number for corresponding traffic transmission. When such requirement is satisfied, the aggregation group is in an UP state, the LACP link is “ON” and ready for use; when such requirement is not satisfied, that is, the number of active interfaces at one end of the aggregation group member link is smaller than the preset minimum active link number, the aggregation group is in a DOWN state, the LACP link is “OFF” and unavailable for use.
The LACP link switching procedure depends on the state of the LACP link aggregation group. In order to monitor a state change of the aggregation group, both ends of the aggregation group periodically transmit a LACPDU (LACP Data Unit) message to each other. After receiving the LACPDU packet, one end of the aggregation group compares information carried by the LACPDU packet, such as system priority, interface priority of the opposite end, with configuration of the local end, in the case of inconformity, adjusts configuration of the local end based on the comparison result. The number of the active interfaces in the aggregation group will change in the process of adjustment. When the number of the active interfaces increases or decreases to a certain degree, the state of the aggregation group will change alternately between the UP and DOWN states, causing the LACP link to switch between “ON” and “OFF”, so that the link appears a flash-off procedure, i.e., the link is OFF and ON. Due to this “flash-off” effect, the user terminal will be “off-line” frequently, and it is needed to re-access network and re-establish data links when communication resumes after a change from “off-line” to “on-line,” which adversely affects normal communication and reduces network service level.
Furthermore, when the active interface in the aggregation group changes to be an inactive interface, the interface is usually configured to be a “dead” interface having no data-transceiving function; however, if the state change of the interface is caused by reasons other than a “physical link failure,” then this can cause the message having been transmitted on the LACP link to be lost and affect normal communication.